The invention relates to a process for treating biogenic residues, particularly sludges, preferably in the area of a clarification plant, as well as an apparatus for carrying out the process with arrangements for drying and incinerating the biogenic residues. Sludges from municipal sewage clarification or industrial plants are subjected at central plants to industrial conditioning for reutilization or conversion into product gas, for example. The sometimes high fraction of biogenic residues in the sludges makes it quite difficult to use them again. Substitution materials added for stabilization generally just increases the volumes of waste for disposal. Disposal itself on dumps and in agriculture is limited in terms of volume the usage thereof is prevented especially because of pollutants in the sludge as well as the trend to biological farming.
In the known processes, drying of the material is generally carried out at high temperatures for subsequent charging into incinerators. Because of the operating conditions, the off-gas from the drying units has a disagreeable odor and it is also fed back to the incinerator. Therefore, the moisture first removed from the process is added back which makes the overall process absurd from the standpoint of the energy balance.
Transporting the sludges to central plants generally entails high costs. One major drawback in particular of the known processes for drying the sludge followed by thermal treatment is particularly the fact that exhaust air generated in the drying process is conducted to the incinerator because of increased fractions of pollutants. Contrary to the desired effect of adding energy to the drying unit, the drying step is carried out here ad absurdum because the removal of water from the process is only apparent since it now has to be heated or evaporated again.
AT 408 509 B, for example, describes a process for drying and incinerating sludge, particularly sewage sludge, using a fluidized bed dryer which is heated with waste gas from the incinerator. The water-enriched air coming from the dryer is recycled to the incinerator. Full evaporation of this air requires the same amount of energy as without drying. Moreover, the rapid and hot drying, usually in fluidized bed driers, causes not inconsiderable bad odors. In order to suppress them as much as possible, the gases generated have to undergo treatment again.
Processes working with thermal disintegration of cells, generally with high-pressure draining and pyrolysis, also need a high fraction of energy for heating. Moreover, these processes also have the problem of odors and thus are not a solution either. Even when a large amount of water is removed, processes providing only for drying the input material do not yield material that can be recycled or dumped.
Finally, known methods for treating sludges at temperatures up to approximately 600° C. do not provide a solution because they do not ensure complete conversion of hazardous materials such as residue from pharmaceuticals.